To reduce the chance that random user space content leaks down the call chain in registers, also clear lower registers on syscall entry:
For 64-bit syscalls, extend the register clearing in PUSH_AND_CLEAR_REGS to %dx and %cx. This should not hurt at all, also on the other callers of that macro. We do not need to clear %rdi and %rsi for syscall entry, as those registers are used to pass the parameters to do_syscall_64(). For the 32-bit compat syscalls, do_int80_syscall_32() and do_fast_syscall_32() each only take one parameter. Therefore, extend the register clearing to %dx, %cx, and %si in entry_SYSCALL_compat and entry_INT80_compat. Cc: Thomas Gleixner <[email protected]> Cc: Andi Kleen <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Al Viro <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Denys Vlasenko <[email protected]> Cc: Brian Gerst <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: "H. Peter Anvin" <[email protected]> Cc: [email protected] Signed-off-by: Dominik Brodowski <[email protected]> --- arch/x86/entry/calling.h | 2 ++ arch/x86/entry/entry_64_compat.S | 6 ++++++ 2 files changed, 8 insertions(+) diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h index be63330c5511..352e70cd33e8 100644 --- a/arch/x86/entry/calling.h +++ b/arch/x86/entry/calling.h @@ -114,7 +114,9 @@ For 32-bit we have the following conventions - kernel is built with pushq %rsi /* pt_regs->si */ .endif pushq \rdx /* pt_regs->dx */ + xorl %edx, %edx /* nospec dx */ pushq %rcx /* pt_regs->cx */ + xorl %ecx, %ecx /* nospec cx */ pushq \rax /* pt_regs->ax */ pushq %r8 /* pt_regs->r8 */ xorl %r8d, %r8d /* nospec r8 */ diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S index 08425c42f8b7..9af927e59d49 100644 --- a/arch/x86/entry/entry_64_compat.S +++ b/arch/x86/entry/entry_64_compat.S @@ -220,8 +220,11 @@ GLOBAL(entry_SYSCALL_compat_after_hwframe) pushq %rax /* pt_regs->orig_ax */ pushq %rdi /* pt_regs->di */ pushq %rsi /* pt_regs->si */ + xorl %esi, %esi /* nospec si */ pushq %rdx /* pt_regs->dx */ + xorl %edx, %edx /* nospec dx */ pushq %rbp /* pt_regs->cx (stashed in bp) */ + xorl %ecx, %ecx /* nospec cx */ pushq $-ENOSYS /* pt_regs->ax */ pushq $0 /* pt_regs->r8 = 0 */ xorl %r8d, %r8d /* nospec r8 */ @@ -365,8 +368,11 @@ ENTRY(entry_INT80_compat) pushq (%rdi) /* pt_regs->di */ pushq %rsi /* pt_regs->si */ + xorl %esi, %esi /* nospec si */ pushq %rdx /* pt_regs->dx */ + xorl %edx, %edx /* nospec dx */ pushq %rcx /* pt_regs->cx */ + xorl %ecx, %ecx /* nospec cx */ pushq $-ENOSYS /* pt_regs->ax */ pushq $0 /* pt_regs->r8 = 0 */ xorl %r8d, %r8d /* nospec r8 */ -- 2.16.3
